Class 5. Aves. Order 1. 8aururce. 453 



of all known Birds, stands nearest to Reptiles. It is characterised 

 firstly by the very long tail consisting of twenty elongate vertebrae, 

 to which the rectrices, known from impressions on the slates, were 

 attached in a single row on either side : and further, by the separa- 

 tion of the metacarpals: by the three well-developed fingers 

 furnished with claws (a point which may be recognised from the 

 form of the last phalanx) : and by the presence of conical teeth on 

 the edges of the jaws. Among other characters it may be noticed 

 that the somewhat thin thoracic ribs have apparently no uncinate 

 processes ; that the cervical ribs are longer ; that the neck and pelvic 

 regions are shorter ; the sternal region, on the other hand, more 

 extensive than in Aves in general (the thoracic vertebrae also appear 

 to have been more freely articulated than is usual) ; that the 

 surfaces of the centra are apparently biplanar (not saddle-shaped) ; 

 and that the lower end of the fibula is complete, not simply ending 

 in a point ; it is even somewhat widened below. From the well- 

 preserved impressions of the large remiges it is proved that 

 Archseopteryx must have been a good flier. Its size was about that 

 of a Pigeon, but it is only known from two specimens, both incomplete ; 

 and the sternum, pelvis, and coracoid are not made out, or only 

 imperfectly. 



Order 2. Odontornithes (Toothed Birds). 



The Toothed Birds, of which several species are known from the 

 Cretaceous of North America, are on the whole very like existing 

 forms, though differing in the possession of teeth upon the edges of 

 the jaws. Some of them (Ichthyornis) possess slightly biconcave 

 centra ; in others {Hesperornis) , the vertebrae are similar to those of 

 living Birds. The mandibular rami are not anchylosed anteriorly. 

 The pelvis is characterised by the fact that the ilium and ischium 

 are not fased posteriorly. For the rest, a considerable variety of 

 forms is grouped under this name : some were able to fly, others 

 possessed rudimentary wings like the Ratitae. 



Order 3. RatitSB {Struthious Birds). 



The most prominent character of this order is the degenerate 

 condition of the wings, which can never be used for flight, 

 and, indeed, are often quite rudimentary. The sternum has no keel. 

 The hind limbs, on which there is usually no hind toe, are generally 

 very powerful, and are used for running; the claws are short and 

 stumpy. The feathers are not arranged in tracts, but are fairly 

 regularly distributed over the whole body (there are, however, naked 

 portions, e.g., on the inner side of the fore limbs in the Ostrich and 



